Incremental test proposal based on the rating of perceived exertion to determine metabolic thresholds and mechanical parameters of free style

Abstracts

A percepção subjetiva de esforço (PSE) é determinada de forma não invasiva e utilizada juntamente com a resposta lactacidêmica como indicadores de intensidade durante teste incremental. Em campo, especialmente na natação, há dificuldades nas coletas sanguíneas; por isso, utilizam-se protocolos alternativos para estimar o limiar anaeróbio. Assim, os objetivos do estudo foram: prescrever um teste incremental baseado na PSE (Borg 6-20) visando estimar os limiares metabólicos determinados por métodos lactacidêmicos [ajuste bi-segmentado (V LL), concentração fixa-3,5mM (V3,5mM) e distância máxima (V Dmáx)]; relacionar a PSE atribuída em cada estágio com a freqüência cardíaca (FC) e com parâmetros mecânicos de nado [freqüência (FB) e amplitude de braçada (AB)], analisar a utilização da escala 6-20 na regularidade do incremento das velocidades no teste e correlacionar os limiares metabólicos com a velocidade crítica (VC). Para isso, 12 nadadores (16,4 ± 1,3 anos) realizaram dois esforços máximos (200 e 400m); os dados foram utilizados para determinar a VC, velocidade de 400m (V400m) e a freqüência crítica de braçada (FCb); e um teste incremental com intensidade inicial baseada na PSE, respectivamente, 9, 11, 13, 15 e 17; sendo monitorados em todos os estágios a FC, lactacidêmia e os tempos de quatro ciclos de braçadas e das distâncias de 20m (parte central da piscina) e 50m. Posteriormente, foram calculadas as velocidades dos estágios, FB, AB, V LL, V3,5mM e V Dmáx. Utilizaram-se ANOVA e correlação de Pearson para análise dos resultados. Não foram encontradas diferenças entre VC, V Dmáx e V LL, porém a V3,5mM foi inferior às demais velocidades (P < 0,05). Correlações significativas (P < 0,05) foram observadas entre VC versus V400m, V Dmáx e V3,5mM; V400m versus V3,5mM e V Dmáx; V Dmáx versus V LL; e no teste incremental entre PSE versus velocidade, [Lac], FC, FB e AB (P < 0,05). Concluímos que a PSE é uma ferramenta confiável no controle da velocidade dos estágios durante teste incremental na natação.

Freqüência cardíaca; Concentração de lactato sanguíneo; Freqüência de braçada; Amplitude de braçada

ORIGINAL ARTICLE

Incremental test proposal based on the rating of perceived exertion to determine metabolic thresholds and mechanical parameters of free style

Propuesta de un test adicional basado en la percepción subjetiva del esfuerzo para determinar los límites metabólicos y los parámetros mecánicos del nado libre

Manoel Carlos Spiguel Lima^I; Pedro Balikian Junior^{I, II}; Cláudio Alexandre Gobatto^III; Jair Rodrigues Garcia Junior^I; Luiz Fernando Paulino Ribeiro^IV

^IFaculdade de Educação Física da UNOESTE, Presidente Prudente, SP

^IIDepartamento de Educação Física da UNESP, Presidente Prudente, SP

^IIIDepartamento de Educação Física da UNESP, Rio Claro, SP

^IVDepartamento de Educação Física da UESC, Ilhéus, BA

^{Correspondence to}

ABSTRACT

The Rating of Perceived Exertion (RPE) is non-invasively determined and used together with lactacidemic analysis as indicator of intensity during incremental test. In field, especially in swimming, due to the difficulty of sample collection, alternative protocols have been used to estimate the anaerobic threshold. Thus, the study aims were: to prescribe one incremental test based on Borg's scale; to estimate metabolic thresholds determined through analysis lactate methods [settling bi-segmented (V_LT), fixed concentration-3.5 mM (V_3.5mM) and maximal distance (V_Dmáx)]; to relate the RPE attributed in each stage with a heart rate (HR) and swimming mechanical parameters [stroke rate (SR), and stroke length (SL)]; to analyze the utilization of the Borg's scale in regularity of velocity increment in test and relate the metabolic thresholds with the critical velocity (CV). Twelve swimmers (16.4 ± 1.3 years old) were subjected to two maximal efforts (200 and 400 meters), the data was used to determine the CV, velocity in 400 meters (V_400m) and critical stroke rate (CSR); and one incremental test with an initial intensity based in RPE, respectively, 9, 11, 13, 15 and 17; the HR, lactacidemia ([Lac]) and the times of four cycles strokes and the distances of 20 m and 50 m, were monitored in all stages. Subsequently, the velocity of the SR, SL, V_LT, V_3.5mM and V_Dmáx stages were calculated. ANOVA and correlation of Pearson were used to analyze the results. Significant differences were not found among VC, V_Dmáx and V_LT, however the V_3,5mM was lower than all velocities (P < 0.05). Significant relationships (P < 0.05) were found among VC versus V_400m, V_Dmáx, V_3.5mM; V_400m versus V_3.5mM and V_Dmáx; V_Dmáx versus V_LL; in incremental test among the RPE versus velocity, [Lac], HR, SR and SL (P < 0.05). Our conclusion was that RPE is a reliable tool for velocity control of stages during incremental test in swimming.

Keywords: Heart rate. Blood lactate concentration. Stroke rate. Stroke length.

RESUMEN

La Percepción Subjetiva del Esfuerzo (PSE) es determinada de forma no invasiva y utilizada juntamente con la respuesta lactacidémica como indicadores de intensidad durante un test de incremento. En campo, especialmente en la natación, hay dificultades en las colectas sanguíneas, por eso se utilizan protocolos alternativos para estimar el límite anaerobio. Así, los objetivos de este estudio fueron: prescribir un test adicional basado en la PSE (Borg 6-20) con el objetivo de estimar los límites metabólicos determinados por métodos lactacidémicos [ajuste bisegmentado (V_LL), concentración fija-3,5 mM (V_3,5mM) y distancia máxima (V_Dmáx)]; relacionar la PSE atribuida en cada etapa con la frecuencia cardíaca (FC) y con los parámetros mecánicos de nado [frecuencia (FB) y amplitud de brazada (AB)], analizar la utilización de la escala 6-20 en la regularidad del incremento de velocidades en el test y correlacionar los límites metabólicos con la velocidad crítica (VC). Para esto, doce nadadores (16,4 ± 1,3 años) realizaron dos esfuerzos máximos (200 y 400 m), los datos fueron utilizados para determinar la VC, velocidad de 400 m (V_400m) y la frecuencia crítica de brazada (FCb); y un test adicional con intensidad inicial basada en la PSE, respectivamente, 9, 11, 13, 15 y 17; siendo monitorizadas en todos las etapas la FC, lactacidemia y los tiempos de 4 ciclos de brazadas y las distancias de 20 m (parte central de la piscina) y 50 m. Posteriormente, se calcularon las velocidades de las etapas, FB, AB, V_LL, V_3,5mM y V_Dmáx. Se utilizó ANOVA y correlación de Pearson para el análisis de los resultados. No se encontraron diferencias entre VC, V_Dmáx y V_LL, sin embargo la V_3,5mM fue inferior a las demás velocidades (P < 0,05). Correlaciones significativas (P < 0,05) fueron observadas entre VC versus V_400m, V_Dmáx y V_3,5mM; V_400m versus V_3,5mM y V_Dmáx; V_Dmáx versus V_LL; y en el test adicional entre PSE versus velocidad, [Lac], FC, FB y AB (P < 0,05). Concluimos que la PSE es una herramienta confiable en el control de la velocidad de las etapas durante el test adicional en la natación.

Palabras-clave: Frecuencia cardíaca. Concentración de lactato sanguíneo. Frecuencia de brazada. Amplitud de brazada.

INTRODUCTION

The lactacidemia response obtained in incremental protocols is a widely used variable in the prescription of exercise intensity in cyclic sports with aerobic predominance. Moreover, it seems to be the best variable in order to identify the exercise suitable intensity⁽¹⁾. Besides the blood lactate analysis, other intensity parameters are usually concomitantly collected during the incremental test, namely: heart rate, oxygen consumption (O₂) and Subjective Perceived Exertion (RPE)^(2-3). The SPE is a non-invasive and practical method for aerobic exercise intensity evaluation^(3-4). It is considered an useful tool for the exercise intensity prescription^(3-4) and a trustful variable for fatigue quantification during test of graduated exercise⁽⁵⁾. However, there is some judgment about its trustfulness during incremental exercise test in treadmill⁽⁶⁾.

There is a consensus that the most trustful methodology in order to determine the intensity of the anaerobic threshold is the lactate maximal steady phase estimate (LMSP), confronting evaluation protocols and methodologies that use the blood lactate in the physical exertion^(7-8). Such protocol requires continuous tests of approximately 30 minutes, performed at different days, which makes its applicability in laboratory or field difficult. In the latter, there is more difficulty due to the lack of or limitation in temperature and humidity control, movement velocity, the manipulation of blood samples materials and the communication with the athletes, especially when the procedures are performed in a pool.

Researchers have been developing alternative protocols in a trial to diminish the presented problems and improve the tests applicability. They highlight the use of the critical velocity model (CV)^(9-10), the determination of the anaerobic threshold through steady concentration of blood lactate (OBLA)^(11-12) and analysis of the swimming mechanical behavior (stroke rate and length), joined with physiological variables^(13-15). Costill et al.⁽¹⁶⁾ presented the concept of stroke index (SB) as a good predictor of the maximal oxygen consumption in trained swimmers. Dekerle et al.⁽⁹⁾, based on the CV concept, used the relation between stroke rate (SR) and time, and developed the critical stroke rate term (CSR), representing a stroke rate in which the swimmer could swim for a long period of time without exhaustion. In a recent study, Papoti et al.⁽¹⁴⁾ were able to determine strength and SR at maximal intensity and in the anaerobic threshold using data acquisition system during exertion in tied swimming.

The SPE response was also observed applying the Borg 620 scale, with linear increase according to power, heart rate (HR) and VO₂ in an incremental test⁽¹⁷⁾. Other researchers have demonstrated that the SPE may be used in order to estimate the lactate threshold (LT)^(18-19) and that it is not affected by the gender^(20-21), training stage^(22-23) and exercise type⁽¹⁸⁾. Thus, the SPE was proposed as being a valid measurement in order to determine the exercise intensity^(4,21,24-25) and a useful tool in the training prescription.

In swimming pools, it is difficult to precisely control the stages velocity during an incremental test the same way it is done in the swimming flume. The alternative incremental protocols for lactecidemia responses analysis require light adjustment in the bottom of the pool or that an evaluator completes the pool's edge distance in order to maintain the established velocities.

Considering reports of increases linearly related between the swimming velocity, swimming physiological parameters and SPE⁽²⁶⁾, the use of the latter instead of the velocity control could simplify the anaerobic threshold evaluation (AT) and associated indices during incremental tests.

Almost all the studies that relate the physiological variables with the SPE, previously determines the stages exertion intensity of the incremental test (velocity, load, etc.) so that the individuals could be later interviewed and attributed the SPE parameters of each stage. Nevertheless, we did not find report of studies that use the SPE in order to establish the intensities of the incremental stages. Thus, our aims were: (1) to determine the intensity of the incremental test stages using the SPE and to analyze the possibility to estimate metabolic thresholds; (2) to analyze the use of the SPE in the control of velocity increase during the stages, joined with the physiological and mechanical responses, during the incremental protocol; (3) to observe the correlations between the SPE, physiological and mechanical variables (stroke rate (SR) and stroke length (SL)) and (4) to verify possible correlations between the different estimation methods of the metabolic thresholds.

METHODOLOGY

Subjects

The study group was consisted of 12 swimmers with age range between 15 and 19 years, trained with 5-6 weekly sessions, daily volume between 4,000 and 8,000 m, with regular training for at least 3,5 years and participation in national and state competitions. The anthropometrical and body composition measures are presented in table 1.

The swimmers received previous information on the experimental procedures and eventual risks and later the clarified consent form was presented and signed by their parents or responsible ones. The protocol and the procedures were approved by the Medical Ethics Committee of the Oeste Paulista University. The evaluated subjects were familiarized with the invasive and non-invasive procedures used, since during the previous training period periodic evaluations were performed in order to determine the training intensities and eight athletes had participated in previous experiments with the same procedures. The 15 points (6-20) Subjective Perceived Exertion Scale (SPE) was presented to the athletes with the instructions prior to all tests, according to the recommendations by Borg⁽²⁷⁾. During 6 months of training the coach used the SPE from one to two times a week in order to quantify the training overload and the athletes performed incremental tests with questions about the SPE after each stage.

Experimental procedures

All evaluations were performed in Olympic swimming pool of 50 m with water temperature between 27^o and 28^oC. The swimming style was the crawl with free warm-up, and tests performance at the athletes training time. The volunteers were asked to avoid intense extra physical activity sessions, not to intake alcoholic drinks during the experimental period and to have their meals two hours prior the test. The swimmers were submitted to maximal sprints at the 200 and 400 m distances, randomly performed with 24 hours of interval between both, and to an incremental test with 200 m stages performed 48 hours after the second maximal sprint.

Critical velocity (CV) and critical stroke rate (CSR)

In order to determine the CV, the time (T200 and T400) of two maximal sprints of 200 and 400 m were registered, which were plotted in a linear regression model between time-distance, resulting in a line whose inclination was considered as the individual CV⁽¹⁰⁾.

A central lane measuring 20 meters of distance was marked in the pool before the maximal exertion, in order to isolate the lapping impulses. The 50 m partials (T50), the time of the 20 m partials (T20) and the time of 4 stroke cycles (T4c) were registered with the aid of digital timers (Casio^®), being later used for the length (SL) and stroke rate (SR) calculation. The critical stroke rate (CSR)⁽⁹⁾ was determined from the linear regression model between SR (min^-1 cycles) and distance, while the SL was determined by the division tof the velocity by the SR.

The heart rate was monitored with Polar frequency meters, S810 model (Polar Electro Oy, Finland). In the end of each sprint the volunteers visualized the Borg's scale (SPE) in order to obtain the real Subjective Perceived Exertion (SPEr).

Incremental test

The incremental protocol consisted of 5 200 m sprints, with 90 seconds pauses for blood samples. The initial intensity and the intensity increases were determined with previous visualization of the 6-20 scale⁽²⁷⁾ of SPE. Thus, the subjective intensity of the test beginning was named prescribed SPE (SPEp) for each of the sprints: 9 (very light), 11 (light), 13 (slightly intense), 15 (intense-heavy) and 17 (very intense). T200, T50, T20, T4c, HR and SPEr were registered, which were later used for the calculation of the velocity of each sprint (V), of SR and SL. After each stage, blood samples from the ear lobes were collected in heparinized capillars, which were immediately transferred to 1,5 mL Eppendorff tubes containing 50 µl of NaF 1% solution and stored in ice for later lactacidemia determination ([Lac]). The reading was performed in electro-enzymatic apparel, YSL 1500 SPORT model (Yellow Springs Co., EUA).

Determination of the lactate threshold velocity through the visual inspection method (V_LT)

Individual swimming velocity (m.s^-1) data and lactate concentration (Lac) (mM) were plotted in order to determine the lactate threshold velocity (V_LT) Two groups of distinct points were obtained through visual analysis of those points and from the sudden increase of the lactacidemia due to the swimming intensity increase. Thus, with the bi-segmentation of the groups of points, two lines were determined through linear regression and the intersection point of the two segments was obtained being equal to the two equations of the lines (y₁ = y₂). Thereby, the x indices corresponding to the inflexion point were found, as well as the V_LT velocity indices.

Determination of the action of the anaerobic threshold velocity through the maximal distance method (V_Dmax)

In order to determine the anaerobic threshold through the maximal distance method (V_Dmax), the lactate-velocity curves suffered polynomial correction of third order (software STATISTIC 6.0). A line between the first and last points was traced and, with the aid of a ruler, the maximal perpendicular distance between the line and the curve was traced. The intersection of this point in the polynomial curve of third order originated the V_Dmax and the corresponding [Lac]⁽²⁸⁾.

Determination of the anaerobic threshold velocity through the 3,5 mM steady concentration (V_3,5mM)

In order to determine the anaerobic threshold intensity corresponding to the 3,5 mM steady lactate concentration (V_3,5mM), the mathematical calculation of linear regression was used with the results obtained in the incremental protocol sprints. The lactate concentration indices above or below 3,5 mM were used in order to interpolate the results with their respective velocities⁽⁸⁾.

SPEr, SR, SL and HR in the different threshold methods

The SPEr, SR and HR parameters in the intensities referring to V_Dmax, CV, and V_3,5mM were determined through the mathematical method of linear regression using the results obtained in the sprints obtained in the incremental protocol for each subject through interpolation.

Statistical analysis

The differences significance between the intensities obtained with the different protocols was determined through variance analysis (one way ANOVA). The Pearson correlation coefficient was used in order to establish the correlations between the variables and the intraclass correlation coefficient was used to test the agreement between the SPEp and SPEr. The significance index of P < 0,05 was adopted and the STASTISTIC 6.0 (Statsoft) software was used.

RESULTS

In tables 2 and 3 the velocities and the stroke rates obtained with invasive and non-invasive methods are presented. It may be observed that only the SR_3,5 of 26,71 ± 3,27 cycles.min^-1 and SR_v400 of 35,11 ± 4,21 cycles.min^-1 were significantly different (P < 0,05) from the critical stroke rate (CSR) of 30,82 ± 3,91 cycles.min^-1 (datum not presented in table 3).

In table 4 the correlations between the intensities of the different protocols and with the performance in the 400 m distance (V₄₀₀) are presented.

The individual correlations between SPEp and the variables determined during the incremental test, velocity (V), lactate concentration ([Lac]), heart rate (HR), stroke length (SL) and stroke rate (SR) varied between r = 0,95-0,99; r = 0,84-1,00; r = 0,94-1,00; r = –0,78-–1,00 and r = 0,90-0,99; respectively. Significant individual correlations were also found between the SR and the variables determined during the incremental test (V, [Lac], SL, and HR) and varied between r = 0,92-0,99; r = 0,91-1,00; r = –0,88-–1,00 and r = 0,91-1,00; respectively.

Figure 1 shows that there was not significant difference between the prescribed Subjective Perceived Exertion (SPEp) and the real (SPEr) during the incremental test effort. Besides that, the intraclass correlation coefficient (95% of reliable interval RI) presented high results for agreement analysis (R = 0,972; RI = 0,84-0,99; P < 0,0001) These results reveal excellent agreement between SPEp and SPEr.

Figure 2 shows the determination coefficients between the SPEp and the heart rate, lactate concentration and velocity variables.

Figure 3 shows the determination coefficients between the SPEp and the stroke length and rate mechanical variables, during the incremental test.

DISCUSSION

Velocity control during the incremental test

The stages velocity during the incremental test linearly increased with the SPEp (figure 2c) and the individual correlations varied between r = 0,95 and 0,99. Therefore, the determination of the subjective intensities using the SPE is reliable in order to establish suitable velocity parameters during the incremental test. Nevertheless, no supporting reference to the presented methodology in our study was found, once the majority of the research uses laboratory tests and/or other sports, and determines the intensities (velocity in treadmill and load in the cycle ergometer) for the physiological data and SPE obtaining, which limits our comparisons.

Similarly to our study, Ueda and Kurokawa⁽²⁶⁾ evaluated six men and four women in the swimming flume, analyzed the correlations between physiological variables (VO₂, HR, [Lac]) with the SPE during incremental test, and observed linear increase between the intensity (arrest) and SPE r = 0,991 for men and r = 0,998 for women). Kang et al.⁽²¹⁾ verified during running and cycling incremental test, linear increase between SPE and the ergometers intensities. Agreeing with the previous study, but using a new exertion perception scale (OMNI) though, Robertson et al.⁽²⁹⁾ and Utter et al.⁽³⁰⁾ found positive correlations between the load and the effort SPE during incremental exercise in treadmill and cycle ergometer. Utter et al.⁽²⁵⁾ evaluated sixty-seven individuals (33 men and 34 women) in treadmill incremental test with the purpose to validate the OMNI exertion perception scale. They reported significant linear increase (P < 0,01) between OMNI and 6-20 Borg's scale with the maximal oxygen percentage (%O₂max) (R² = 0,74 and 0,77) for men and (R² = 0,72 and 0,73) for women, respectively, and between the OMNI and SPE scales (R² = 0,92) for both sexes. Garcin and Billat⁽²⁾ obtained high correlation between O₂max velocity (vO₂max) with the SPE (r = 0,91) in twelve well-trained runners during incremental test on 400 meters track.

In another interesting study, Marriott and Lamb⁽³¹⁾ performed two rowing ergometer tests in nine male rowers. The first incremental test (estimation test) was performed in order to obtain the SPE, HR data and average power of each stage performed until the voluntary fatigue. The second test (production test) was performed with intensities using the SPE 6-20 scale in irregular order (15, 11, 17, 13 and 19). The results demonstrated correlation coefficients between SPE and average power (watts) in the estimation and production tests (r = 0,96 and r = 087, respectively, P < 0,01). The lowest correlation obtained in the production test was possibly due to the SPE intensities irregularly established. In a similar study, Eston et al.⁽³²⁾ performed treadmill test with 16 men and 12 healthy women, finding in the graduated exercise test (estimation) significant correlation coefficient between %O₂max and SPE (r = 0,91 for men and r = 0,87 for women), and in the production test (with SPE indices of 9, 13 and 17) with correlation coefficients between %O₂max and SPE of r = 0,93 for men and r = 0,89 for women. These results corroborate the results of our study which presented individual correlations of r = 0,95 to 0,99 between the SPEp and velocity (m.s^-1) during the incremental test.

Determination of metabolic thresholds

The incremental test using the SPEp made the metabolic thresholds estimation possible, as well as the analysis of the correlation coefficient between the used methods (tables 2 and 3). Significant correlations between the V_3,5mM and CV, V_Dmax and V_LT, and between V_Dmax and CV (r = 0,80; r = 0,92 and r = 0,69; respectively, P < 0,05) were found. It was not possible to identify the metabolic thresholds in three athletes, due to the atypical disposition of the lactate-velocity curve points used for the V_LT and V_Dmax estimation, through visual inspection after the curves adjustments. On the other hand, the V_3,5mM was obtained through linear regression for all subjects. Thus, the non-estimation of the V_LT and V_Dmax thresholds for the three subjects was not due to the proposed protocol, but to the obtained data instead.

Physiological variables behavior during the incremental test

The heart rate (HR) responded linearly with the SPEp increase (R² = 0,999; figure 2a) during the incremental test, and the individual correlations varied between r = 0,94 and 1,00. Similar data were presented by Ueda and Kurokawa⁽²⁶⁾ who found significant correlation between arrest (N) and HR, VO₂ and HR; SPE and HR for men (r = 0,99; 0,99 and 0,99) and women (r = 0,99; 0,99 and 0,99; respectively). In the study by Marriott and Lamb⁽³¹⁾, the correlation coefficient in the SPE estimation test (incremental test) was of r = 0,95 and in the production irregular test (using the SPE for intensity determination) was of r = 0,75.

Demura and Nagasawa⁽³³⁾ evaluated 10 healthy students in cycle ergometer, and analyzed the physiological responses with the SPE parameters during incremental test until fatigue and in an active recovery of 25 minutes. The results showed significant correlations between HR and SPE during the test (r = 0,99) and in the recovery (r = 0,97).

Other studies showed significant correlations between the SPE and metabolic demand measured through the oxygen consumption and HR^(17,34), however, the HR may be directly influenced by several factors, among which we may highlight medication, measuring difficulty⁽³⁵⁾, room temperature influence⁽³⁶⁾ and the lower number of heart beats in water in comparison to land⁽³⁷⁾. Such factors may generate imprecision in the intensity control during the exercise.

The lactate concentration is considered the most sensitive local factor of metabolic stress⁽¹⁹⁾ and reflects in the SPE increase during exercise^(22,24). According to other studies^(26,38), one may observe that the lactecidemia response during the incremental test correlated with the SPEp (r = 0,84-1,00 and r² = 0,996; P < 0,05, figure 2b). However, even facing the significant correlations, we should mention that the SPE is influenced by central (oxygen consumption, ventilation and HR) and local parameters (lactate concentration). Thus, the best correlations between lactate and SPE are found during incremental tests^(26,38). In recent study, Green et al.⁽³⁾ did not find correlation between lactate and SPE during test with steady load with duration of sixty minutes in cycle ergometer. The researchers evaluated physically active subjects of both sexes, and the results showed decrease of the lactacidemia and SPE increase, confirming that there is dissociation between lactate and SPE, and that other factors significantly contribute to the SPE increase in continuous tests with steady load. Mercer⁽³⁸⁾ conducted a study in order to analyze the SPE reproducibility related to the blood lactate in fourteen women divided in two groups according to their physical ability (high O₂max and moderate O₂max). The SPE relation with the lactate threshold (SPE_LT), the steady 2 mM lactate concentration (SPE₂), 2,5 mM (SPE_2,5) and 4 mM (SPE₄) were determined, and the intraclass correlation coefficient for the group with high O₂max of r = 0,97; r = 0,97; r = 0,97 and r = 0,72; and for the moderate VO₂max group of r = 0,83; r = 0,96; r = 0,96 and r = 0,90 respectively, were found. No significant differences between the groups in relation to the SPE_LT, SPE₂, SPE_2,5 and SPE₄ were found.

In another study, Kolkhorst et al.⁽³⁹⁾ evaluated ten subjects during incremental test in treadmill in order to analyze the effect of different inclinations (+5%, 0% and –5%) in SPE response related to the 2mM and 4mM lactate steady concentrations. The lowest SPE was related to the 2 mM steady lactate concentration during the incremental test with +5% inclination comparing to the 0% and –5% inclinations (P < 0,05). On the other hand, the SPE related to 4mM steady lactate concentration was not different between incremental tests with +5%, 0% and –5% inclinations. The authors reported that there were not significant differences between the relative oxygen consumption and the respiratory coefficient (RC) in the three different inclinations related to the 2 mM and 4 mM concentrations. On the other hand, the HR related to 2 mM in the incremental test with –5% inclination was significantly higher than 0% and +5% (P < 0,05), as well as the treadmill velocity related to the steady 2 mM and 4 mM lactate concentration was lower during the +5% test comparing to the remaining inclinations (P < 0,05). These results showed a possible correlation between the SPE, HR and treadmill velocity, however, the authors did not perform correlations between these variables, which limits the comparison with our results.

Mechanical variables behavior during the incremental test

In this study significant individual correlations were found between HR and the velocity (V), lactate concentration ([Lac]), stroke length (SL) and heart rate (HR) variables which varied between r = 0,92-0,99; r = 0,91-1,00; r = –0,88-–1,00 and r = 0,91-1,00; respectively. During the incremental test, the increase between the SPEp and the SR was exponential and the significant determination coefficient (R² = 0,98) (figure 3b). In the study by Wakayoshi et al.⁽¹⁵⁾ conducted with tem well-trained swimmers in the swimming flume, significant linear correlations were found between cubic velocity and SR of r = 0,89 (P < 0,05) at r = 0,99 (P < 0,01) during the swimming savings test, which used 5 or 6 submaximal intensities. The CSR calculated using the 200 and 400 meters distances was not significantly different from the SR determined in 30 minutes continuous test (SR₃₀), there was significant correlation (r = 0,86; P < 0,01) between the two frequencies, though. The authors reach to the conclusion that CSR underestimated in 3,9% the SR₃₀ and that the CV and CSR indices may be used for the aerobic training load control and the swimming technique.

Dekerle et al.⁽⁹⁾ and Wakayoshi et al.⁽⁴⁰⁾ define the CSR as a stroke rate that may be kept for a long period of time without fatigue. In an evaluation of the 8 male well-trained swimmers, Dekerle et al.⁽⁹⁾ observed that the O₂ and the SR did not change in sub-thresholds of 30% to 60% of the velocity of the O₂max. Contrarily, significant increases in the O₂ and SR were found in supra-threshold intensities of 80% and 100% of the O₂max velocity. Thus, it was demonstrated that the anaerobic intensity emphasizes swimming technique damage in order to maintain the required velocity. Therefore, such intensity would be impossible for the swimming technique training with the aim to improve the mechanical efficiency. It was also stated that the suitable SR or intensity to the improvement of the swimming technique should be anaerobic sub-threshold or CSR.

The presented results in figure 3b show significant determination coefficient between SL and SPEp (R² = 0,995), and negative individual correlations ranging from r = –0,88 to –1,00 for the SR and SL. Keskinen et al.⁽⁴¹⁾ did not find significant differences between the SR determined in 25 and 50 meters swimming pool, however, the SL was significantly longer in the 25 meters pool, with differences ranging from 1,8% up to 8,2% during the 200 meters progressive sprints. The SR in the aerobic and anaerobic threshold determined in both pools, did not present significant difference either. An issue to be considered in the study is that the authors makes use of the velocity obtained in the progressive sprints and relates SR and SL. The velocity in the 25 meters pool was slightly higher comparing to the 50 meters one, which may be due to the bigger amount of laps, which seems to cause the overestimated result of the SL in the 25 meters.

One of the few longitudinal studies of the analysis of swimming mechanical parameters was performed by Wakayoshi et al.⁽⁴²⁾. The aerobic training effect was observed for six months in the velocity variables (V), SR, SL and [Lac] in eight swimmers. The pre and post-tests consisted of a 400 meters maximal sprint (Vmax) and three submaximal ones in the 85%, 90% and 95% velocities of the Vmax obtained in the first 400 meters sprint. Significant increase in the threshold velocity was observed (VOBLA) and maximal velocity (Vmax) between the pre and post-training (P < 0,05). The increase of the post-training V85%, V90% and V95% was due to the increase of the SR and decrease of the SL. Nonetheless, the Vmax increased facing a SL increase, being the SL increase more visible in the final 150 meters (6th, 7th and 8th stage of 50 meters). As expected, the [Lac] in the Vmax was significantly lower in the post, comparing to the pre-training.

CONCLUSION

The SPE is a reliable parameter in the control of the exercise intensity during incremental test in swimming, with no need of velocity control during each stage of the test in a pool. Moreover, the test made the estimate of the metabolic thresholds used in the study possible. It is important to mention that the athletes were familiarized with the SPE for a 6 months period, which seems to have contributed for a good intensity control using the SPE. Nevertheless, the number of studies using the intensity determination and establishing increases with the SPE during the incremental test is scarce. Further research with the aim to obtain data which may confirm the established proposal is still needed. Thus, the intensity determination methodology through the SPE in the incremental tests will be able to be applied in athletes of different previous knowledge of the 6-20 scale and different physical ability levels. A reliability and reproducibility test is still necessary in order to reassure the efficiency of the proposed model.

REFERENCES

Received in 21/10/05.

Final version received in 17/3/06.

Approved in 15/5/06.

All the authors declared there is not any potential conflict of interests regarding this article.

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Publication Dates

• Publication in this collection
  18 June 2007
• Date of issue
  Oct 2006

History

• Accepted
  15 May 2006
• Received
  17 Mar 2006